Communication Efficiency of Quantum SystemsThis report presents a method for evaluating the theoretical performance of quantum communication systems based on the communication efficiency parameter, β = P/NoR. For Gaussian systems, β represents the minimum average amount of energy required to decipher a bit of information, with zero error, in the presence of white noise of spectral density No. For certain quantum systems, the Gaussian result is directly applicable with No replaced by hv. In general, β is recognized to be the minimum number of average (photon) events required to decipher a bit of information with zero error. To make comparisons with Gaussian systems, the parameter K is introduced and hv/K becomes the effective Gaussian spectral density of the quantum system. Several systems are considered in addition to the capacity bound for the narrow-band quantum channel introduced by Gordon. Unlike the Gaussian channel, there is no lower bound on β as the bandwidth-to-data-rate ratio, α, is increased. Thus β can be continually decreased at the expense of average data rate. For large values of α, PPM direct detection asymptotically approaches the lower bound for β |
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additive Gaussian noise additive noise approach the Gordon background noise BAND PPM bandwidth-to-data-rate ratio Bhet Bhom bit of information Bppm central limit theorem communication efficiency decipher a bit decreasing Kn digital direct detection direct detection systems duty cycle effective Gaussian temperature Electronics Research Center energy required figure of merit Gaussian channel Gaussian noise channel Gaussian systems Gordon bound heterodyne system homodyne system hv/K information with zero KT n hv limit theorem arguments lower bound minimum number narrow-band photon channel narrow-band PPM system narrow-band quantum channel noise spectral density number of photons Optical Communications optical filter P/hvB Performing Organization plotted in Figure Poisson presence of white quantum channel introduced quantum communication systems quantum detector quantum mechanical quantum noise quantum system quantum-limited signal-to-noise ratio required to decipher shown system bandwidth Theoretical B-efficiency Theoretical values value of Kn white noise wideband PPM channel wideband PPM systems zero error